Modern industrial, commercial, aerospace and military systems depend critically on reliable pumps for fluid handling. The trends in fluid handling systems are toward smaller, more distributed and more portable systems for increasing uses in instrumentation and control.
Although important advances in pump technology have been made in the past few decades, progress has reached saturation in terms of ability to reduce pump size, weight and power requirements. There is a significant gap between the technology for conventional pumps, including the so-called imicropumps, i and pumps that are based on microelectronics technology.
The pumping capability of these micropumps is in one to tens of microliters per minute range. This makes them useful for applications such as implantable systems for drug delivery or micro dosage in chemical analysis systems but such pumping speeds are many orders of magnitude smaller than those required in sampling applications.
A number of United States patents have been granted on apparatus and devices generally relating to microvalve construction and control. For example, U.S. Pat. No. 5,082,242 to Bonne et al describes a microvalve that is an integral structure made on one piece of silicon such that the device is a flow through valve with inlet and outlet on opposite sides of the silicon wafer. The valves are closed by contact with a valve seat where surfaces must be matched in order to avoid degradation of valve performance. Two patents, U.S. Pat. Nos. 5,180,623 and 5,244,527 are divisional patents relating to the first mentioned patent.
Another family of patents describe fluid control employing microminiature valves, sensors and other components using a main passage between one inlet and exit port and additionally a servo passage between inlet and outlet ports. The servo passage is controlled by a control flow tube such that tabs are moved electrostatically. U.S. Pat. No. 5,176,358 to Bonne et al teaches such a fluid regulating device, while divisional U.S. Pat. Nos. 5,323,999 and 5,441,597 relate to alternative embodiments.
An additional concept is disclosed by Wagner et al in the June, 1996, edition of the IEEE Journal, pages 384-388, in which two buckled Si/SiO.sub.2 membranes spanning air filled cavities having enclosed driving electrodes. A coupled membrane system is disclosed in which a first silicon membrane is switched by electrostatic force which, in turn, presses air through a channel to push the second silicon membrane up.
In both of these patented systems and in the concept described by Wagner et al, silicon semiconductor chips are employed. Silicon technology is, in fact, a host for a number of microsensors. The possibility of fabricating fully integrated systems led to the development of some of the above described valves and the like. However, the displacements available at the microscale and the materials available in silicon technology are not the best for such applications. The achievable pumping rates are very small (.mu.l to ml/min) at the best. Additionally the structures tend to become complicated and expensive. Of major concern also is the fact that silicon is not compatible with many biological materials, thus eliminating virtually an entire field of end use.
Current sampling pumps for vapor and particle detection are much larger than the instruments they support. In order to be effective for many missions, the sampling rate should be comparable to human breathing, i.e., 10 liters per minute (lpm) or more. The pumps must supply this flow against pressure drops of one psi or more, corresponding to pneumatic output loads exceeding a watt and input power requirements exceeding ten watts. Current system using rotating motors are power hungry, noisy and have limited lifetimes. Mesoscopic pumps with no rotating or sliding parts and high electrical-to-pneumatic conversion efficiencies would be able to dramatically increase the capabilities and effectiveness of military systems that detect chemical, biological, explosive and other agents.
Several versions of these mesopumps are disclosed in U.S. Pat. No. 5,836,750, by Cleopatra Cabuz, entitled Electrostatically Actuated Mesopump Having a Plurality of Elementary Cells. The mesopumps described therein and other more primitive pumps all use a plurality of chambers, such as, for example, three or four chambers, each of which having one diaphragm. While admirably suited for their intended use, some applications may, in the future, be limited by the size and compactness of these prior art mesopumps. Also, in some applications for these mesopumps, the presence of lateral channels and the resulting dead space again limit their applicability. Present day prior art mesopumps also require molding of extra ports to provide pressure relief for unused diaphragm surfaces.
It would be of great advantage in the art if a more compact, lighter weight mesopump could be provided for any given fluid pumping rate.
It would be another great advance in the art if mesopumps could be developed with inlet and outlet ports in the center of the chamber to eliminate lateral channels.
Yet another advance would be achieved if mesopumps could be developed which have no need for molding extra ports for pressure relief.
Other advantages will appear hereinafter.